Phosphate doping as a promising approach to improve reactivity of Nb2O5 in catalytic activation of hydrogen peroxide and removal of methylene blue via adsorption and oxidative degradation

This study is devoted to the evaluation of the influence of phosphate dopants on the reactivity of Nb₂O₅-based nanomaterials in the combined catalytic activation of H₂O₂ and the elimination of methylene blue (MB) from an aqueous solution via adsorption and chemical degradation. For this purpose, several niobia-based catalysts doped with various amounts of phosphate were prepared by a facile hydrothermal method and subsequent calcination. Phosphate doping was shown to strongly enhance the ability of Nb₂O₅ to activate H₂O₂, as well as to adsorb and degrade MB. The most pronounced differences in the reactivity of the parent Nb₂O₅ and phosphate-doped samples were observed under strongly acidic conditions (pH ~ 2.4), at which the most active modified catalysts (Nb/P molar ratio = 5/1) was approximately 6 times more efficient in the removal of MB. The observed enhancement of reactivity was attributed to the increased generation of singlet oxygen ¹O₂, which was identified as the main oxidizing agent responsible for efficient degradation of MB. To our knowledge, it is the first report revealing that phosphate doping of Nb₂O₅ resulted in an improved activity of niobia in the adsorption and degradation of organic pollutants.

Unraveling the Origin of Enhanced Activity of the Nb2O5/H2O2 System in the Elimination of Ciprofloxacin: Insights into the Role of Reactive Oxygen Species in Interface Processes

The overlooked role of reactive oxygen species (ROS), formed and stabilized on the surface of Nb₂O₅ after H₂O₂ treatment, was investigated in the adsorption and degradation of ciprofloxacin (CIP), a model antibiotic. The contribution of ROS to the elimination of CIP was assessed by using different niobia-based materials in which ROS were formed in situ or ex situ. The formation of ROS was confirmed by electron paramagnetic resonance (EPR) and Raman spectroscopy. The modification of the niobia surface charge by ROS was monitored with zeta potential measurements. The kinetics of CIP removal was followed by UV-vis spectroscopy, while identification of CIP degradation products and evaluation of their cytotoxicity were obtained with liquid chromatography-mass spectrometry (LC-MS) and microbiological studies, respectively. Superoxo and peroxo species were found to significantly improve the efficiency of CIP adsorption on Nb₂O₅ by modifying its surface charge. At the same time, it was found that improved removal of CIP in the dark and in the presence of H₂O₂ was mainly determined by the adsorption process. The enhanced adsorption was confirmed by infrared spectroscopy (IR), total organic carbon measurements (TOC), and elemental analysis. Efficient chemical degradation of adsorbed CIP was observed upon exposure of the Nb₂O₅/H₂O₂ system to UV light. Therefore, niobia is a promising inorganic adsorbent that exhibits enhanced sorption capacity toward CIP in the presence of H₂O₂ under dark conditions and can be easily regenerated in an environmentally benign way by irradiation with UV light.

Intermolecular interactions of tetracyanoethylene (TCNE) and fumaronitrile (FN) with minor amines: A combined UV–Vis and EPR study

In this paper, the nature of interactions between two cyanocarbons—tetracyanoethylene (TCNE) and fumaronitrile (FN)—and a series of four secondary amines possessing a general formula C4HxN (x = 5–11) is thoroughly scrutinized. For all of the TCNE–amine pairs, tricyanovinylation (TCV) reaction is observed; however, only for pyrrole, it is accompanied with a visible charge-transfer (CT) complex formation—no such chemical individuals, characteristic for TCNE, have been noticed for aliphatic and alicyclic amines. On the contrary, FN forms such complexes with all the amines studied. Interestingly, a rather unexpected reaction of FN with alicyclic amines has been observed. The recorded electron paramagnetic resonance (EPR) spectra indicate the presence of both TCNE●− and FN●− radicals in the analyzed samples, assigned to a complete charge (electron) transfer process within the CT complexes, whose efficiency can be additionally enhanced by photoirradiation. The origination of the former radical, whose presence is observed also in the TCNE–diethylamine mixture, is as well proposed to result indirectly from the TCV reaction, occurring for this system. Finally, the superhyperfine structure of EPR spectra, indicating the existence of some secondary interactions of the radicals with surrounding compounds, is discussed. Formation of CT complexes and tricyanovinylates has been investigated and characterized with UV–Vis spectroscopy, while the presence of (cyano)radicals in the analyzed mixtures has been evidenced by (photoinduced) EPR measurements. Interpretation of the experimental results is also supplemented with computer simulations including density functional theory calculations.

Relevance of the electron transfer pathway in photodynamic activity of Ru(II) polypyridyl complexes containing 4,7-diphenyl-1,10-phenanthroline ligands under normoxic and hypoxic conditions

The purpose of this study was to investigate the correlation between the spectroscopic and photophysical properties of Ru(II) polypyridyl complexes and their photodynamic activity in vitro. A series of Ru(II) polypyridyl complexes with 4,7-diphenyl-1,10-phenanthroline (dip) and 2,3-bis(2-pyridyl)quinoxaline (dpq) and its derivatives were synthesized and characterized regarding their photophysical, biological, and photodynamic properties. The complexes were evaluated not only in the context of ¹O₂ generation but also regarding other types of reactive oxygen species (ROS) to assess the possibility of Ru(II) complexes to induce phototoxicity via various ROS using fluorescence and EPR spectroscopy. The compounds were found to be moderately cytotoxic with IC₅₀ values ranging from 1 to 35 μM and retained their cytotoxic activity under hypoxic conditions. The unraveled phototoxic activity is based mainly on the generation of H₂O₂ and ¹O₂, highlighting the importance of electron-transfer processes in the observed photodynamic activity of Ru polypyridyl complexes. A combination of photodynamic activity with cytotoxicity under decreased dioxygen concentrations may help overcome the current photodynamic therapy (PDT) limitation. The findings highlight the need for broadening the scope of tested Ru-based photosensitizers.

Analysis of NH3 -TPD Profiles for CuSSZ-13 SCR Catalyst of Controlled Al Distribution - Complexity Resolved by First Principles Thermodynamics of NH3 Desorption, IR and EPR Insight into Cu Speciation*

NH₃ temperature-programmed desorption (NH₃ -TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NO_x . Herein, we propose an interpretation of NH₃ -TPD results, which takes into account the temperature-induced dynamics of NH₃ interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH₃ adsorption on single Cu²⁺ , Cu⁺ , [CuOH]⁺ centers, dimeric [Cu-O-Cu]²⁺ , [Cu-O₂ ^2- -Cu]² species, segregated CuO nanocrystals and Brønsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH₃ desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH₃ -TPD experiment. Thus, a rigorous interpretation of the NH₃ -TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers.

Enhanced adsorption and degradation of methylene blue over mixed niobium-cerium oxide - Unraveling the synergy between Nb and Ce in advanced oxidation processes

Formation of reactive oxygen species (ROS) via H₂O₂ activation is of vital importance in catalytic environmental chemistry, especially in degradation of organic pollutants. A new mixed niobium-cerium oxide (NbCeO_x) was tailored for this purpose. A thorough structural and chemical characterization of NbCeO_x along with CeO₂ and Nb₂O₅ reference materials was carried out using TEM/STEM/EDS, SEM, XRD, XPS, EPR, UV-vis and N₂ physisorption. The ability of the catalysts to activate H₂O₂ towards ROS formation was assessed on the basis of EPR and Raman measurements. Catalytic activity of the oxides was evaluated in degradation of methylene blue (MB) as a model pollutant. Very high activity of NbCeO_x was attributed to the mixed redox-acidic nature of its surface, which originated from the synergy between Nb and Ce species. These two properties (redox activity and acidity) ensured convenient conditions for efficient activation of H₂O₂ and degradation of MB. The activity of NbCeO_x in MB degradation was found 3 times higher than that of the commercial Nb₂O₅ CBMM catalyst and 240 times higher than that of CeO₂. The mechanism of the degradation reaction was found to be an adsorption-triggered process initiated by hydroxyl radicals, generated on the surface via the transformation of O₂^-•/O₂^2-.

Correction: Stability of Cu(II) complexes with FomA protein fragments containing two His residues in the peptide chain

Correction for 'Stability of Cu(ii) complexes with FomA protein fragments containing two His residues in the peptide chain' by Monika Katarzyna Lesiów et al., Metallomics, 2019, 11, 1518-1531, DOI: 10.1039/C9MT00131J.

ROS-mediated lipid peroxidation as a result of Cu(ii) interaction with FomA protein fragments of F. nucleatum: relevance to colorectal carcinogenesis

The ability of the studied FomA protein fragments of Fusobacterium nucleatum (Fn) with copper(ii) ions (Cu(ii)-Ac-KGHGNGEEGTPTVHNE-NH2 (1Cu) and its cyclic analogue Cu(ii)-cyclo(KGHGNGEEGTPTVHNE) (2Cu)) to induce reactive oxygen species (ROS) generation, as a result of red-ox processes, was determined by UV-Vis, luminescence methods, spin trapping and cyclic voltamperometry. The contribution of 1O2 and ˙OH to DNA degradation was proved using gel electrophoresis. Furthermore, the pronounced generation of ROS by mouse colon carcinoma cells (CT26) stimulated by both copper(ii) complexes was confirmed. A fluorescence method allowed the total amounts of ROS generated inside the CT26 cells to be detected, while the spin trapping technique proved that free radicals mainly attached to the membrane surface. These last results are in agreement with the data obtained from the ICP-MS method, which demonstrates that 1Cu and 2Cu complexes are not efficiently accumulated inside the cell. Furthermore, the role of ROS in lipid peroxidation was established. The above-mentioned factors may clearly indicate the contribution of ROS generated by the studied copper(ii) complexes to colonic cell damage, which can lead to a carcinogenesis process. This study may be an important step to recognize and understand the mechanism of colon cancer initiation.

Stability of Cu(ii) complexes with FomA protein fragments containing two His residues in the peptide chain

The coordination process of Cu(ii) ions with FomA protein fragments ofFusobacterium nucleatumcontaining two histydyl residues was determined.

Ein Programm zur Diagnosenverschlüsselung im Dialogverkehr

Zur Unterstützung der Diagnosendokumentation bieten sieh die Methoden der Klartextverarbeitung oder der Verschlüsselung an. Die Klartextverarbeitimg mit ihren Problemen, vor allem im multi-disziplinären Einsatz, erscheint der Diagnosenverschlüsselung noch nicht überlegen. Es wurde daher eine EDV-gestützte Diagnosenverschlüsselung in Form eines Bildschirmdialogs entwickelt, die den ICD-kompatiblen »Klinischen Diagnosenschlüssel« (KDS) mit einer Erweiterung durch ein Suffix und eine Synonymkennimg benutzt. Die frei eingegebenen Diagnosentexte werden von Stop Wörtern befreit und aus den übrigen Wörtern die ersten fünf Zeichen (Infix) als Suchmerkmale in einer Datenbank genutzt. Alle im KDS enthaltenen Diagnosen, die die gesuchten Infixe enthalten, werden zur Auswahl mit dem Lichtstift am Bildschirm angeboten. Zur hierfür benötigten Schnittmengenbildung wird ein schnelles Direktzugriffsverfahren eingesetzt. Im KDS fehlende Diagnosen können vorläufig verschlüsselt und anschließend ergänzt werden. Blättern, Korrigieren und Direkteingabe einer bekannten Schlüsselausprägung des klinischen Diagnosenschlüssels sind möglich. Das Programm ist Teil eines umfassenden Informationssystems für ein Großklinikum.

Paramagnetic dioxovanadium(IV) molecules inside the channels of zeolite BEA--EPR screening of VO2 reactivity toward small gas-phase molecules

Interaction of small gas-phase molecules (NO, N2O, O2, CO) with VO2 radicals inside the channels of a dealuminated SiBEA zeolite was investigated by means of electron paramagnetic resonance (EPR), infrared (IR), and mass (QMS) spectroscopies to provide direct insights into the chemistry of a unique paramagnetic state of vanadium - VO2 molecules. A facile way of forming VO2 inside the channels of SiBEA via thermal reduction of VO2(+) precursor cations was shown. Dioxovanadium(IV) was identified based on its unusual EPR signal which, as compared with the typical monooxovanadium(IV) (VO(2+) cation), is featured by rhombic symmetry and a positive Aiso value leading to a hyperfine splitting as large as 32 mT. VO2 molecules exhibit reducing properties transforming N2O and O2 into vanadium intrachannel cage adducts comprising of reactive oxygen species (O(-) and O2(-), respectively). Interaction with CO led to its oxidation to CO2, while paramagnetic NO acted as a scavenger for VO2 radicals producing diamagnetic adducts. The observed reactivity was rationalized in terms of spin-pairing, electron transfer, and oxygen transfer processes. As a result new chemical pathways of vanadium reactivity were demonstrated which were not observed so far either in the homogeneous molecular systems or supported vanadium materials.

Gravity-dependent differentiation and root coils in Arabidopsis thaliana wild type and phospholipase-A-I knockdown mutant grown on the International Space Station

Arabidopsis roots on 45° tilted agar in 1-g grow in wave-like figures. In addition to waves, formation of root coils is observed in several mutants compromised in gravitropism and/or auxin transport. The knockdown mutant ppla-I-1 of patatin-related phospholipase-A-I is delayed in root gravitropism and forms increased numbers of root coils. Three known factors contribute to waving: circumnutation, gravisensing and negative thigmotropism. In microgravity, deprivation of wild type (WT) and mutant roots of gravisensing and thigmotropism and circumnutation (known to slow down in microgravity, and could potentially lead to fewer waves or increased coiling in both WT and mutant). To resolve this, mutant ppla-I-1 and WT were grown in the BIOLAB facility in the International Space Station. In 1-g, roots of both types only showed waving. In the first experiment in microgravity, the mutant after 9 days formed far more coils than in 1-g but the WT also formed several coils. After 24 days in microgravity, in both types the coils were numerous with slightly more in the mutant. In the second experiment, after 9 days in microgravity only the mutant formed coils and the WT grew arcuated roots. Cell file rotation (CFR) on the mutant root surface in microgravity decreased in comparison to WT, and thus was not important for coiling. Several additional developmental responses (hypocotyl elongation, lateral root formation, cotyledon expansion) were found to be gravity-influenced. We tentatively discuss these in the context of disturbances in auxin transport, which are known to decrease through lack of gravity.

Magnetic Properties of Monomer and Dimer Tetrahedral VO(x) Entities Dispersed on Amorphous Silica-based Materials: Prediction of EPR Parameters from Relativistic DFT Calculations and Broken Symmetry Approach to Exchange Couplings

Molecular structures of the isolated tetrahedral oxovanadium(IV) and bridged μ-oxo-divanadium(IV) complexes hosted by the clusters mimicking surfaces of amorphous silica-based materials were investigated using density functional theory (DFT) calculations. Principal values of the g and A tensors for the monomer vanadyl species were obtained using the coupled-perturbed DFT level of theory and the spin-orbit mean-field approximation (SOMF). Magnetic exchange interaction for the μ-oxo bridged vanadium(IV) dimer was investigated within the broken symmetry approach. An antiferromagnetic coupling of the individual magnetic moments of the vanadium(IV) centers in the [VO-O-VO](2+) bridges was revealed and discussed in detail. The coupling explains pronounced decrease of the electron paramagnetic resonance signal (EPR) intensity, observed for the reduced VO(x)/SiO(2) samples with the increasing coverage of vanadia, in terms of transformation of the paramagnetic monomer species into the dimers with S = 0 ground state.

Spin ground state and magnetic properties of cobalt(II): relativistic DFT calculations guided by EPR measurements of bis(2,4-acetylacetonate)cobalt(II)-based complexes

The spin ground state of the core ion and structure of the bis(2,4-acetylacetonate)cobalt(II) model complex and its synthetic aqua and ethanol derivatives, Co(acac)(2)L(n), (L = EtOH, H(2)O), were examined by means of density functional theory (DFT) calculations supported by electron paramagnetic resonance (EPR) measurements. Geometry optimizations were carried out for low-spin (doublet) and high-spin (quartet) states. For the Co(acac)(2) complex two possible conformations, a square-planar and a tetrahedral one, were taken into account. For all structures relative energies were calculated with both "pure" and hybrid functionals. The calculated data were complemented with the results of the EPR investigations carried out at liquid helium temperature, allowing for definite assignment of the high-spin state for the Co(acac)(2)(EtOH)(2) complex. However, because of the unresolved spectral features, only effective g-values could be assessed, whereas the zero-field splitting parameters (ZFS) were calculated by means of the spin-orbit mean field (SOMF) relativistic DFT method for which direct spin-spin (SS) and spin-orbit coupling (SOC) contributions were quantified.

Co2+/Co0 redox couple revealed by EPR spectroscopy triggers preferential coordination of reactants during SCR of NOx with propene over cobalt-exchanged zeolites

Catalytic reduction of NOx with propene over Co2+ -exchanged beta and ZSM-5 zeolites occurs with formation of zero-valent cobalt; NOx preferentially adsorbed on Co2+ plays the role of a metal reducing agent while ligation of propene is favored for Co(0) centers.

DFT calculations of magnetic parameters for molybdenum complexes and hydroxymethyl intermediates trapped on silica surface

Density functional theory (DFT) calculations of EPR parameters and their structure sensitivity for selected surface paramagnetic species involved in oxidative dehydrogenation of methanol over silica grafted molybdenum catalyst were investigated. Two surface complexes, Mo(4c)/SiO2 and {O(-)-Mo(4c)}/SiO2, as well as *CH2OH radical trapped on the SiO2 matrix were taken as the examples. The spin-restricted zeroth order regular approximation (ZORA) implemented in the Amsterdam Density Functional suite was used to calculate the electronic g tensor for those species. The predicted values were in satisfactory agreement with experimental EPR results. Five different coordination modes of the *CH2OH radical on the silica surface were considered and the isotropic 13C, 17O, and 1H hyperfine coupling constants (HFCC) of the resultant surface complexes were calculated. Structure sensitivity of the HFCC values was discussed in terms of the angular deformations caused by hydrogen bonding with the silica surface.

Relativistic Density Functional Calculations of EPR g Tensor for η{CuNO}11 Species in Discrete and Zeolite-Embedded States

Spin-unrestricted zeroth order regular approximation (ZORA) and the scalar relativistic method based on Pauli Hamiltonian implemented in the Amsterdam Density Functional suite were used to calculate the electronic g tensor for isolated covalent {CuNO}(11) and electrostatic {q-NO}(1) species and for various model molecular and nonmolecular {CuNO}(11)-containing systems, epitomizing copper nitrosyl cage adducts in the ZSM-5 zeolite. The predicted g tensor values using the ZORA/VWN scheme were in satisfactory agreement with experimental EPR results. Relativistic, diamagnetic, and paramagnetic contributions to the calculated g tensor were quantified. The nature of the observed Deltag shifts was discussed in terms of the molecular orbital contributions due to the magnetic field-induced couplings and their structure sensitivity. The influence of basis set and exchange-correlation functional on the results was also briefly evaluated.

Spectroscopy and Computations of Supported Metal Adducts. 1. DFT Study of CO and NO Adsorption and Coadsorption on Cu/SiO2

Interactions of the CO and NO molecules with the Cu(II) and Cu(I) isolated sites on the amorphous silica surface are investigated by means of density functional theory (DFT) methods within the finite cluster model approach. The clusters of silica of increasing nT size (T = Si) are used, with n from 2 to 6. The Cu(II) sites are characterized by calculated g-tensors and hyperfine coupling constants (HFCCs) and compared with experiment. On this basis, the three-coordinated complexes are the most plausible. Due to the charge transfer from the silica "ligand", the metal charge shrinks and the spin density is distributed over silanol and siloxy groups up to 50%. The reduced sites are exclusively two-coordinated. Strong interaction of CO with Cu(I)-nT sites (31-39 kcal/mol) gives rise to the formation of carbonyl adducts with planar coordination around copper. The population of the ligand pi system shifts downward the stretching frequency in agreement with experiment. Reaction with a second CO molecule gives a geminal dicarbonyl of very uniform structure independent of the site. Carbonyl complexes with Cu(II) are less stable and of tetrahedral coordination of the metal. Accumulation of the positive charge on the complex along with sigma overlap with d orbitals locates the calculated CO stretching frequency above free molecule value. NO molecule is preferably bound to the Cu(II)-nT sites, forming a tetrahedral complex with tilted adsorbate and NO stretching frequency blue-shifted with respect to the free molecule value. The full set of electron paramagnetic resonance (EPR) parameters and vibrational frequencies for the copper(I) mononitrosyl, {CuNO}(11), though not observed experimentally, are predicted and compared to the same magnetophore inside the ZSM-5 zeolite. The interaction energies show that in the CO/NO reaction mixture adsorption is selective and allows discrimination between Cu(I) and Cu(II) sites. However, for the Cu(I) complex, formation of mixed-ligand structures of the {Cu(CO)(NO)}(11) type is possible.

Application of the Genetic Algorithm Joint with the Powell Method to Nonlinear Least-Squares Fitting of Powder EPR Spectra

The application of the stochastic genetic algorithm (GA) in conjunction with the deterministic Powell search to analysis of the multicomponent powder EPR spectra based on computer simulation is described. This approach allows for automated extraction of the magnetic parameters and relative abundances of the component signals, from the nonlinear least-squares fitting of experimental spectra, with minimum outside intervention. The efficiency and robustness of GA alone and its hybrid variant with the Powell method was demonstrated using complex simulated and real EPR data sets. The unique capacity of the genetic algorithm for locating global minima, subsequently refined by the Powell method, allowed for successful fitting of the spectra. The influence of the population size, mutation, and crossover rates on the performance of GA was also investigated.

Paramagnetic species on catalytic surfaces--DFT investigations into structure sensitivity of the hyperfine coupling constants

Structure sensitivity of the hyperfine coupling constants was investigated by means of DFT calculations for selected surface paramagnetic species. A *CH2OH radical trapped on silica and intrazeolite copper nitrosyl adducts encaged in ZSM-5 were taken as the examples. The surface of amorphous silica was modeled with a [Si5O8H10] cluster, whereas the zeolite hosting sites were epitomized by [Si4AlO5(OH)10]- cluster. Three different coordination modes of the *CH2OH radical were considered and the isotropic 13C and 1H hyperfine constants of the resultant van der Waals complexes, calculated with B3LYP/6-311G(d), were discussed in terms of the angular deformations caused by hydrogen bonds with the cluster. The magnetic parameters of the eta1-N[CuNO]11 and eta1-O[CuNO]11 linkage isomers were calculated at the BPW91/LanL2DZ and 6-311G(df) level. For the most stable eta1-N adduct a clear dependence of the spin density distribution within the Cu-NO moiety on changes in the Cu-N-O angle and the Cu-N bond distance was observed and accounted for by varying spin polarization and delocalization contributions.